Means for handling electrophotographic transfer sheets



April 28, 1970 L |NBA ET AL 3,508,824

MEANS FOR HANDLING ELECTROPHOTOGRAPHIC TRANSFER SHEETS Filed March 8,1967 RlCHARD K. LEINBACH THADDEUS SWANKE INVENTORS fMu/M ATTORNEYS BY MM372%)- United States Patent 1 3,508,824 MEANS FOR HANDLING ELECTROPHOTO-GRAPHIC TRANSFER SHEETS Richard K. Leinbach and Thaddeus Swanke,Rochester,

N.Y., assignors to Eastman Kodak Company, Rochester, N .Y., acorporation of New Jersey Filed Mar. 8, 1967, Ser. No. 621,565 Int. Cl.G03g 15/00 US. Cl. 355-3 9 Claims ABSTRACT OF THE DISCLOSURE Anelectrophotographic reproducing apparatus, with an electricallyconductive guide plate for conveying a transfer sheet from aphotoconductive member to a fixing station without disturbing a loosepowder image on the transfer sheet. The transfer sheet is stripped fromthe photoconductive member by advancing the photoconductive memberthrough a bend near the guide plate to cause the leading edge of thetransfer sheet to be separated from the photoconductive member by theresistance of the transfer sheet to bending. The guide plate iselectrostatically attractive to the transfer sheet. The guide plate ispositioned to contact the non-image side of the separated leadingportion of the transfer sheet.

' The leading portion of the transfer sheet is guided to This inventionrelates to means for handling an electrophotographic transfer sheethaving a loose powder image on one surface thereof. More specifically,this invention relates to means for stripping a transfer sheet from amoving photoconductive member and for guiding the transfer sheet to afusing station without disturbing the loose powder image.

In transfer electrophotography, typically, an electrostatic image isformed on a photoconductive surface and that image is developed byapplication of charged toner powder. The powder image thus formed istransferred to a transfer sheet placed in face contact with the powderimage. This transfer can be accomplished by electrostatically chargingthe non-image side of the transfer sheet so as to attract the tonerparticles from the photoconductive surface to the sheet. The transfersheet bearing the loose powder image is then removed from thephotoconductive surface and conveyed to a fixing station where thepowder image is fixed to the sheet, for example by heat or vapor fusion.

The means for stripping the transfer sheet from the photoconductivesurface after the transfer step and for conveying that transfer sheet tothe fusing station are critical, because the powder image should not becontacted or disturbed. Prior to the fusing step, the powder imageloosely adheres to the transfer sheet by electrostatic attraction, andany physical contacting of the image may displace the powder and smearthe image.

The stripping of the transfer sheet. has been accomplished several waysin the prior art, such as by stripper blades or synchronized blasts fromair jets. Some of these prior art means are complicated by therequirement of synchronization or movement, and others contact the imageside of the transfer sheet.

3,508,824 Patented Apr. 28, 1970 The prior art has also employed avariety of mechanical means for conveying the transfer sheet, such asbelt conveyors or chain conveyors carrying mechanical sheet grippers.Drive rollers, of course, are usually not practical because they contactthe transfer sheet on both sides and smear the image. The belt conveyorsdo not provide positive sheet attachment, and are limited as to locationin the copier since they rely on gravity. The chain conveyors requiretripping mechanisms or synchronization of the sheet grippers. Moreover,these devices all require their own driving means.

It is an object of this invention to provide means for stripping atransfer sheet in electrophotographic reproducing apparatus from amoving flexible photoconductive member and for conveying the transfersheet to a sheet receiving means without disturbing a powder imagecarried by the transfer sheet and without the use of additional drivemeans or moving parts, other than the moving photoconductive member.

It is another object of this invention to provide means for guiding theleading portion of a transfer sheet by electrostatic force from aphotoconductive member to a fusing station in electrophotographicreproducing apparatus as the trailing portion of the transfer sheet isadvanced by the photoconductive member.

These and other objects are attained by a sheet handling meanscomprising two cooperating components; namely, stripping means and guidemeans. The stripping means separates the transfer sheet from theflexible photoconductive member by moving the photoconductive memberthrough a bend which is sufliciently sharp to cause a leading portion ofthe transfer sheet to separate from the photoconductive member due tothe resistance of the transfer sheet to bending. The stripping of thetransfer sheet may be assisted by attraction of the sheet to the guidemeans, which is located near the bend and is electrostaticallyattractive to the transfer sheet. The guide means comprises a conductiveplate that is permanently positioned to contact the non-image side ofthe separated leading portion of the transfer sheet and to guide thatleading portion by electrical attraction to a sheet receiving means,usually the fixing station, as the sheet is moved forward throughdecreasing contact with the moving photoconductive member. The guideplate may be made electrically attractive to the transfer sheet in anydesired manner, but when the transfer sheet carries an electrostaticcharge, it is preferable that the guide plate be grounded to provideelectrostatic bias with respect to the sheet. This invention alsocomprehends the above guide means in combination with any other meansfor stripping the leading portion of the transfer sheet from thephotoconductive member.

In the accompanying drawings:

FIG. 1A is a diagrammatical side view of the one embodiment of theinvention.

FIG. 1B is a perspective view of the embodiment shown in FIG. 1A.

FIG. 2 is a diagrammatical side view of another embodiment of theinvention.

According to. one embodiment of this invention, as illustrated in FIGS.1A and 1B, a flexible photoconductive member 1, comprising aphotoconductive insulating layer 2 and a conductive layer 3, advances inthe direction indicated by the arrow through a plurality of processstations (not all shown) in an electrophotographic reproducingapparatus.

In a typical electrophotographic reproducing apparatus, the severalprocessing stations in the path of movement of the photoconductivemember, which are not shown and do not form part of the invention, maybe functionally described as follows:

A charging station, at which an electrostatic charge is deposited on thephotoconductive member;

An exposure station, at which a light image to be reproduced isprojected onto the photoconductive member to dissipate the charge in theexposed areas of the photoconductive member and thereby form a latentelectrostatic image; and

A developing station, at which a toner powder having an electrostaticcharge opposite to that of the latent image is brushed or cascaded overthe surface of the photoconductive member, whereby the toner particlesadhere to the electrostatic latent image to from a powder image.

The three processing stations described above are only one example ofseveral known electrophotographic reproducing processes, in which aloose powder image is formed on a photoconductive member. In suchprocessing apparatus, the loose powder image on the photoconductivemember is transferred to a transfer sheet, which is then stripped fromthe photoconductive member and conveyed to a fixing station where theloose powder image is fixed onto the transfer sheet.

In FIGS. 1A and 1B the photoconductive member 1 carries on one surface aloose powder image 5, which has been formed by any of the knownelectrophotographic methods. A transfer sheet 6 is fed by rollers 7 ontothe powder image 5. The photoconductive member I carrying the powderimage and the transfer sheet 6 advances under a corona charger 8, whichplaces an electrostatic charge opposite to that of the toner powder onthe surface of the transfer sheet opposite the powder image. The powderimage 5 is thereby caused to electrostatically adhere to the transfersheet 6. Following this powder image transfer, the flexiblephotoconductive member 1 is caused to go around a bend at the desiredstripping point. This bend is defined by the location of a roller 4,around which the flexible photoconductive member 1 travels. When thephotoconductive member 1, carrying the sheet 6 with the powder image 5,starts into the bend at roller 4, the stiffness of the transfer sheet 6causes it to resist bending. The bend is made sufficiently sharp, asdetermined by the diameter of roller 4, that the stiffness of thetransfer sheet 6 overcomes the electrostatic attraction between thetransfer sheet 6 and the photoconductive member 1, and separation of aleading portion of the transfer sheet is initiated. There is a tendencyfor retacking of the transfer sheet 6 to occur when the separatedportion becomes long enough to overcome the stiffness of the sheet 6. Toprevent this retacking, a conductive plate 9 is positioned with one end10 adjacent to the stripping point. Since the conductive plate 9 isconnected to ground at 11, the highly charged sheet material 6 iselectrostatically attracted to the grounded plate. This electrostaticattraction assists the stripping of the transfer sheet 6 from thephotoconductive member and draws the separated portion of the transfersheet into contact with conductive plate 9. The separated leadingportion of the transfer sheet 6 is thereby caused to electrostaticallyadhere to the conductive plate 9, while the trailing portion of thetransfer sheet is still in electrostatic contact with thephotoconductive member 1 which continues to move and advance thetransfer sheet 6 along the surface 12 of the conductive plate 9. Sincethe transfer sheet 6 is at least partially insulating, its high chargedoes not drain olf rapidly to the conductive plate. Therefore, the biasbetween the sheet and the plate is maintained for a sufficient period oftime to permit the leading portion of the transfer sheet 6 to be guidedto a. sheet receiving means 13, usually the fusing station, adjacent tothe end 14 of plate 9. The plate may be curved to guide the sheet in anydesired direction, so that flexibility in locating the fuser isprovided.

Any fusing means may be used in the practice of this invention, but thepowder image should not be disturbed prior to fusing. An example of afuser which would work satisfactorily with this guide plate is describedin US. Patent 2,701,765. It will be seen that the powder image 5 isnever contacted or disturbed in any way by the subject stripping andconveying means.

The present invention can be used in combination with rigidphotoconductive members or plates as well as with flexiblephotoconductors. As seen in FIG. 2, the photoconductor 1 is supported ona rigid drum support 15. The sheet feed and transfer steps of theprocess are identical to those described for FIG. 1. After the transferstage, the leading portion of the transfer sheet 6 is stripped from thephotoconductor 1 by any desired means, such as, for example, a pick-01fblade 16. When the leading portion of transfer sheet 6 is stripped fromthe rigid photoconductor 1, it is attracted to the conductive guideplate 9 in the same manner, as in the FIG. 1 embodiment, by theelectrostatic bias between the grounded conductive plate 9 and thecharged transfer sheet. The plate 9 then functions as a curved guide andas an electrostatic support for the transfer sheet 2, as it is advancedby the moving photoconductor 1.

In either of the embodiment described in FIGS. 1 and 2, it is preferablethat the end-portion 10 of the plate 9 adjacent the stripping point besomewhat curved, so that good contact is established with the separatedleading portion of the transfer sheet 6 after stripping, regardless ofthe angle at which the sheet approaches the plate.

In both embodiments, described in the drawings and above, the guideplate 9 is grounded and the transfer sheet is electrostatically charged.This method of providing a bias is entirely satisfactory regardless ofwhether the charge on the sheet material 6 is positive or negative. Itis also immaterial in the practice of this invention whether the guideplate 9 is grounded or connected to an electric potential, so long asthere is an electric attraction between the guide plate 9 and thetransfer sheet. The use of an electric potential for providing bias isnecessary if the transfer sheet does not carry an electrostatic charge.However, grounding is preferable because of simplicity, when thetransfer sheet carries an electrostatic charge deposited by the transferelectrode.

It should be evident that any method of stripping the leading edge ofthe transfer copy sheet 6 may be used in the practice of this invention,but the stripping means should not disturb or contact the powder image5. If the photoconductive member is not continuous, the transfer copysheet could be superimposed on it with the leading edge of the sheetoverhanging the leading edge of the photoconductive member, so that thefree leading edge of the sheet is available to contact the guide means.If the photoconductor is continuous or if it is not desirable orpractical to provide an overhang of the transfer sheet, many othermechanical separators are suitable. Suction rollers, air jet strippersor mechanical blade strippers are some examples of known means forinitiating the stripping of the leading edge of the transfer sheet 6.However, when mechanical strippers are used, the guide plate 9 should bepositioned to electrically attract the transfer sheet 6 away from thestripping initiator 16, before the image area of the transfer sheet iscontacted. Of course, when a flexible photoconductive member is used,stripping of the transfer sheet is preferably accomplished automaticallyby providing the relatively sharp bend in the flexible member, describedin FIGS. 1A and 1B as a feature of the invention.

Although the invention has been described in considerable detail withreference to certain preferred embodiments thereof, it will beunderstood that variations and modifications can be effected withoutdeparting from the spirit and scope of the invention as describedhereinabove and as defined in the appended claims.

We claim:

1. In electrophotographic and similar reproducing apparatus having amovable flexible photoconductive member, means to form an electrostaticlatent image on the photoconductive member, means to develop theelectrostatic latent image with toner powder, means to superimpose atransfer sheet on the developed powder image, means to transfer thepowder image to a surface of the superimposed transfer sheet creating anelectrostatic charge on said transfer sheet, and means to fix thetransferred powder image onto the transfer sheet, the improvementcomprising:

means for advancing the flexible photoconductive member in a path havinga bend of sufficient curvature to cause a leading portion of a transfersheet to which an unfixed powder image has been transferred, to beseparated from the movable flexible photoconductive member, and

electrically conductive, grounded means positioned to contact theleading portion of a transfer sheet so separated, on the surfaceopposite to the image-bearing surface for electrically attracting andguiding the separated leading portion toward said fixing means while thetransfer sheet is advanced by the movable photoconductive member.

2. In electrophotographic and similar reproducing apparatus of the typehaving a movable flexible photoconductive member, means for forming anelectrostatic latent image on the photoconductive member, means fordeveloping the electrostatic latent image with toner powder, means forsuperimposinga transfer sheet on the developed powder image, means fortransferring the powder image to a surface of the transfer sheet, andmeans for fixing the transferred powder image onto the transfer sheet,the improvement comprising:

means for advancing said flexible photoconductive member in a pathhaving a bend of sufficient curvature to cause a leading portion of atransfer sheet to which an unfixed powder image has been transferred tobe separated from the movable flexible photoconductive member, and

grounded conductive guide means positioned to contact the leadingportion of the transfer sheet so separated, on the surface opposite tothe image carrying surface for electrostatically supporting and guidingsaid transfer sheet toward said fixing means.

3. In electrophotographic and similar reproducing apparatus of the typehaving a movable photoconductive member, means for moving saidphotoconductive member along an operative path, means for forming anelectrostatic latent image on the photoconductive member, means fordeveloping the electrostatic latent image with toner powder, means forsuperimposing a transfer sheeton the developed powder image, means forimparting an electrostatic charge to the transfer sheet to effecttransfer of the powder image to the contingent surface of the transfersheet, and means for fixing the transferred powder image to the transfersheet, the improvement comprising:

means for causing separation of a leading portion of the transfer sheetfrom the movable photoconductive member after transfer of a powder imageto the sheet, and

grounded, electrically conductive guide means, positioned to contact theleading portion of the transfer sheet so separated on the surfaceopposite to the image carrying surface, for electrostatically supportingand guiding the separated transfer sheet during movement toward saidfixing means.

4. In electrophotographic and similar reproducing apparatus having amovable flexible photoconductive member, means for forming anelectrostatic latent image on the photoconductive member, means fordeveloping the electrostatic latent image with toner powder, means forsuperimposing-a transfer sheet on the developed powder image, means forimparting an electrostatic charge to the superimposed transfer sheet toeffect the transfer of the powder image to the contingent surface of thetransfer sheet, and means for fixing the transferred powder image ontothe transfer sheet, an improved device for separating an image-bearingtransfer sheet from said photoconductive member and for guiding theseparated transfer sheet toward said fixing means with minimaldisturbance of the powder image, "said device comprising:

a grounded electrically conductive guide member located between saidpowder image transferring means and'said fixing means, and

means for advancing said photoconductive member in a path having a bendlocated sufficiently close to said guide member and with sufiicientcurvature to cause a leading portion of the transfer sheet to beseparated from the portion of the photoconductor moving around saidbend, whereby the leading portion of the transfer sheet is supported andguided by said guide member for movement towards said fixing station.

5. A device 'for handling a transfer sheet in electrophotographic %andsimilar apparatus, said transfer sheet being electrostatically chargedand carrying on one surface thereof an unfixed powder image, said devicecomprising:

receiving means;

a flexible photoconductive surface for supporting said transfer sheet;

means for ad vancng said photoconductive surface along a path having abend of sufficient curvature to cause a leading portion of the imagecarrying transfer sheet supported thereon to be separated from saidphotocon'diictive surface; and

grounded conductive guide means, positioned to contact said separatedleading portion of said transfer sheet on the surface opposite saidimage carrying surface, for electrostatically supporting and guidingsaid leading portion of said transfer sheet towards said receivingmeans.

6. Means for handling an electrostatically charged transfer sheet inelectrophotographic and similar apparatus, the transfer sheet carryingon one surface thereof an unfixed powder image, said handling meanscomprising:

receiving means;

a movable surface for supporting and driving said transfer sheet;

means for separating a leading portion of said transfer sheet from themovable surface; and

electrically grounded guide means positioned to contact said separatedleading portion of the transfer sheet on the surface opposite to saidimage carrying surface for electrostatically supporting and guiding saidleading portion of the transfer sheet towards the sheet receiving meanswhile the transfer sheet is driven by the movable surface.

7. A device for use in electrophotographic apparatus to effectseparation of a transfer sheet having a powder image electrostaticallycarried thereon from a moving photoconductive web which supports thetransfer sheet, said powder image having been transferred to thetransfer sheet from said web, said device comprising:

(a) means for moving said web along a path having a bend of suflicientcurvature to cause the leading end of the transfer sheet supportedthereon to separate from the web; and

(b) electrically grounded means located with respect to said web movingmeans at a position such that the electrostatic charge on the separatedleading end of a transfer sheet will cause the side of the leading endof the sheet opposite the powder image to move into contact with saidelectrically grounded means.

8. The invention defined in claim 7 wherein said electrically groundedmeans comprises a guide surface for 7 trically grounded means comprisesa guide surface fro directing a separated transfer sheet which isattracted thereto toward subsequent treating stations of theelectrophotographic apparatus.

9. The invention defined in claim 7 wherein said moving means moves saidweb and supported sheet along a flat path upstream from said bend.

References Cited UNITED STATES PATENTS 3,351,340 11/1967 Levine 226-94XR 3,139,013 6/1964 Graves 3553 NORTON ANSHER, Primary Examiner L. H.MCCORMICK, 111., Assistant Examiner U.S. Cl. X.R. 27118

